Free machining austenitic stainless steel

ABSTRACT

A free machining austenitic stainless steel consisting essentially of from a trace up to 0.15 percent carbon, from 2 to 10 percent manganese, from 4 to 13 percent nickel, from 10 to 20 percent chromium, from 0.5 to 3 percent copper, from 0.10 to 0.40 percent sulfur, 2 percent max. silicon, and 0.10 percent max. nitrogen, the balance essentially iron and residual impurities.

atet 1 Ferree, J r.

FREE MACHINING AUSTENITIC STAINLESS STEEL Inventor: Joseph A. Ferree,Jr., Natrona Heights, Pa.

Allegheny Ludlum Industries, Inc., Pittsburgh, Pa.

The portion of the term of this patent subsequent to Aug. 12, 1986, hasbeen disclaimed.

Filed: June 18, 1969 Appl. No.: 834,477

Related U.S. Application Data Division of Ser. No. 740,807, May 29,1968, Pat. No. 3,460,939, which is a continuation-in-part of Ser. No.418,991, Dec. 17, 1964, abandoned.

Assignee:

Notice:

References Cited UNITED STATES PATENTS 11/1940 Krivobok 75/128 A 3/1948Lee 75/128 A LOG DRILL LIFE 1*June 10, 1975 2,495,731 l/l950 Jennings75/128 A 2,697,035 12/1954 Clarke 75/125 2,775,519 12/1956 B]oom..75/125 2,802,755 8/1957 Bloom.. 75/128 2,848,323 8/1958 Harris 75/1253,152,934 10/1964 Lula 75/125 3,401,035 9/1968 Moskowitz 75/1253,401,036 9/1968 Dulis 75/125 3,437,478 4/1969 Moskowitz 75/1283,460,939 8/1969 Ferree 75/125 FOREIGN PATENTS OR APPLICATIONS 1,458,0429/1966 France 12/1967 United Kingdom Primary ExaminerL. Dewayne RutledgeAssistant ExaminerArthur J. Steiner Attorney, Agent, or FirmVincent G.Gioia; Robert F. Dropkin [57] ABSTRACT A free machining austeniticstainless steel consisting essentially of from a trace up to 0.15percent carbon, from 2 to 10 percent manganese, from 4 to 13 percentnickel, from 10 to 20 percent chromium, from 0.5 to 3 percent copper,from 0.10 to 0.40 percent sulfur, 2 percent max. silicon, and 0.10percent max. nitrogen, the balance essentially iron and residualimpurities.

6 Claims, 6 Drawing Figures 8% MANGANESE 6 MANGANESE 4 MANGANESE PERCENTCOPPER PATENTEDJUH 10 I915 8 8 5 5 9 SHEET 1 F /6. I0. I

8% MANGANESE 6 MANGANESE 4 MANGANESE LOG OR/LL LIFE [.5 I l I PERCENTCOPPER I FIG. lb

LOG OP/LL LIFE /.a l l 1 1 I PERCENT COPPER INVENTOR. JOSEPH A. FERPEE,JR.

By /vWLA4iS-QW Attorney FREE MACHINING AUSTENITIC STAINLESS STEEL ThisApplication is a division of previously copending application Ser. No.740,807, filed May 29, 1968, now US. Pat. No. 3,460,939, issued Aug. 12,1969, which in turn is a continuation-in-part of now abandoned,previously copending, application Ser. No. 418,991, filed Dec. 17, 1964.

This invention relates to ferrous base alloys, and more particularly toa free machining, austenitic stainless steel.

Of the many different grades of stainless steel, AISI Type 303 is theconventional, standard type free machining austenitic stainless steel.This type of stainless steel, which is a chromium-nickel type, contains,as principal alloying components, from about 17 to 19 percent chromium,from 8 to 10 percent nickel,'0.l5 maximum carbon, 2 percent maximummanganese and 1 percent maximum silicon, with up to about 0.20 percentphosphorus; up to 0.60 percent molybdenum and .60 percent zirconium maybe added for some applications. It has been found, however, that anaustenitic stainless steel with substantially improved free machiningproperties over those of AISI Type 303 is provided in achromium-nickel-manganese-copper type austenitic stainless steel towhich sulfur is added as a free machining element. Additionally, it hasbeen found that the same chromium-manganese-copper system will provide astainless steel of equivalent machinability to that of the Type 303stainless steel with about half of the amount of sulfur that would berequired in the Type 303 stainless steel. Since the sulfur content islower the corrosion resistance is improved, as are the hot and coldworking properties, inasmuch as the detrimental effects of sulfur oncorrosion resistance and hot and cold working are well known.

It is therefore a principal object of this invention to provide animproved free machining austenitic stainless steel.

A more particular object of this invention is to provide an austenitic,free machining stainless steel which will have machinability comparableto that of the AISI Type 303 at reduced sulfur levels, and improvedmachinability at comparable sulfur levels.

A still further, more specific object is to provide an improved freemachining austenitic stainless steel wherein the alloying elements arebalanced to produce optimum corrosion resistance and free machiningproperties.

These and other objects, together with a fuller understanding of theinvention, may be had from reference to the following description takenin conjunction with the accompanying drawing in which:

FIG. 1 (a) is a graph showing the effect of copper at various manganeselevels on the machinability of stainless steels of this invention;

FIG. I (b) is a composite of the lines of FIG. 1 (a)- showing thiseffect of copper at the average manganese content;

FIG. 2 (a) is a graph showing the effect of manganese at various copperlevels on the machinability of stainless steels of this invention;

FIG. 2 (b) is a composite of the lines of FIG. 2 (a) showing this effectof manganese at the average copper content; I

FIG. 3 (a) is a graph showing the effect of nickel at various copperlevels on the machinability of stainless steels of this invention, and

FIG. 3 (b) is a composite of the lines of FIG. 3 (a) showing the effectof nickel at the average copper content.

The free machining characteristics of any ferrous tain maximum freemachining characteristics. 1 have found that by properly controllingthealloying elements of chromium nickel, manganese, copper and sulfur, anaustenitic stainless steel can be provided which will have materiallyimproved machining characteristics over AISI Type 303 stainless steel atcomparable sulfur levels, comparable machining characteristics atreduced sulfur levels, although the machining characteristics will notbe as good as the free machining grades of ferritic stainless steels.

The alloy according to this invention will have from a trace up to about0.15 percent maximum carbon,

from about 2 percent to about 10 percent manganese,

from about 4 percent to about 13 percent nickel, from 10 to 20 percentchromium, from 0.5 percent to about 3 percent copper, from 0.10 percentto about 0.40 percent sulfur, up to 2 percent silicon up to about 0.10percent nitrogen, and optionally up to about 0.60 percent molybdenum and0.60 percent zirconium; other elements may be added to obtain specificcharacteristics of stainless steel.

Table 1 below lists the composition and machinability, as measured bydrill testing, of various types of free machining stainless steels, somewithin the scope of this invention and some not. The drill tests areperformed in the following manner:

Slabs of material to be tested are provided which are three-fourths inchthick and have opposed flat machined faces. The slabs are chucked in aconventional drill press, and a series of holes is drilled in each slabwith twist drills. The twist drills for such testing were manufacturedby the Cleveland Twist Drill Company of Cleveland, Ohio, and are similarto conventional twist drills but are finished to the closest possibletolerances. In the present case the drills were 1 diameter drillsmanufactured from AISI Grade M-l high speed tool steel. The drill speedfor the present tests was 3,050 R.P.M., and the feed was 0.005 inch perrevolution. The feed was automatically accomplished by a screw driveincorporated in the drill press to maintain accuracy. Conventionalsulfurized cutting oil was used .as a lubricant and maintained at aconstant flow throughout the tests. Holes were drilled at leastone-eighth inch apart to minimize the effect of work hardening radiatingfrom the holes as they were drilled. The tests on the slabs of each heatcontinued until a wear land of 0.015 inch, as measured by a calibratedmicroscope, was worn on the cutting edge of the drill used for the test,and this was considered the end point of the test. The total inchesdrilled was then calculated by multiplying the number of holes drilledby three-fourths inch (the 3 4 thickness of the slabs), and this Inchesof holes the purpose of determining the effect of each of these drilledthe value l1sted 1n Table 1. elements on the machinab1lity. Themachmabillty of TABLE I 1 11 111 1V V VI VII VIII Drill Log Drill LogDrill Life Heat No. %Cu %Mn %Ni %S Life (1) Life (2) Standardized(3)1727 Res.(4) 1.00 8.97 .30 59 1.771 1.771 1462 do. 1.10 9.03 .34 531.724 1.552 1732 do. 1.99 7.07 .33 109 2.037 1.908 1672 do. 1.84 9.05.33 79 1.898 1.769 1805 do. 1.99 9.15 .24 22 1.342 1.600 1731 do. 2.009.00 .33 107 2.029 1.900 1457 do. 2.09 9.10 .33 112 2.049 1.920 1459 do.2.14 9.10 .32 87 1.940 1.854 1458 do. 2.16 9.09 .33 80 1.903 1.774 1750do. 2.26 8.92 .35 110 2.041 1.826 1734 do. 1.98 10.84 .30 65 1.813 1.8131735 do. 3.98 9.01 .34 21 1.322 1.160 1846* do. 4.12 6.18 .32 65 1.8131.727 1847* do. 4.00 7.96 .30 25 1.398 1.398 1848* do. 5.92 8.02 .30 1002.000 2.000 1743 do. 5.92 8.74 .33 58 1.763 1.634 1849* do. 6.06 6.34.31 61 1.785 1.742 1761 do. 6.00 6.92 .32 1.477 1.391 1850* do. 7.906.24 .28 132 2.121 2.207 1851* do. 7.97 8.09 .28 109 2.037 2.123 1762do. 8.00 7.07 .35 44 1.644 1.429 1764 do. 8.20 9.20 .31 74 1.869 1.8261774 do. 10.08 5.08 .27 41 1.613 1.742 1778 do. 10.02 6.87 .25 30 1.4771.692 1730 .98 2.03 8.99 .33 43 1.634 1.505 1852* 1.09 4.04 6.25 .35 1612.207 1.992 1856* 1.14 4.12 7.83 .35 78 1.892 1.677 1740 1.04 5.73 6.93.30 47 1.672 1.672 1860* 1.17 6.07 6.30 .31 1.978 1.935 1863* 1.23 6.008.10 .32 172 2.236 2.150 1865* 1.20 7.94 6.42 .29 163 2.212 2.255 1869*1.07 8.04 7.84 .31 183 2.263 2.220 1469 1.50 2.20 6.65 .32 48 1.6811.595 1467 1.45 2.13 6.85 .33 101 2.004 1.875 1677 1.55 5.25 4.80 .30 411.613 1.613 1679 1.56 5.47 5.02 .33 112 2.049 1.920 1857* 1.77 4.09 7.85.35 2.130 1.915 1673 1.75 5.45 5.55 .30 178 2.250 2.250 1760 1.75 5.955.15 .30 97 1.987 1.987 1739 1.76 5.90 5.32 .25 75 1.875 2.090 1466 1.756.10 5.40 32 164 2.215 2.129 1474 1.70 6.40 5.65 32 231 2.364 2.2781870* 1.73 7.97 8.00 29 143 2.155 2 198 1324 1.90 .49 7.00 33 41 1.613 1484 1325 1.93 1.05 7.02 33 119 2.076 1 947 1473 2.06 1.12 7.15 34 1842.265 2 093 1326 1.99 1.09 9.14 34 106 2.025 1 853 1728 1.92 1.01 11.1530 59 1.771 1771 1729 1.95 1.94 7.32 33 82 1.914 1 785 1502 1.98 2.076.66 37 132 2.121 1 820 1472 1.98 2.20 6.73 34 145 2.161 1 989 1468 V1.95 2.20 6.75 38 60 1.778 1 434 1470 l 1.98 2.20 7.15 34 186 2.270 2098 1471 1.98 2.20 7.20 35 90 1.954 1 739 1737 1.88 2.13 9.10 31 801.903 1 860 1854* 1.94 4.00 6.25 32 129 2.11 1 2.025 1736 1.88 3.9611.00 33 113 2.053 1.924 1759 2.05 6.00 4.82 30 11 1 2.045 2.045 17512.00 6.38 6.00 31 133 2.124 2.081 1861* 1.90 6.08 6.34 31 171 2.2332.190 1864* 1.95 6.00 8.12 33 216 2.335 2.206 1765 1.96 8.30 9.25 29 1132.053 2.096 1855* 2.54 4.08 6.05 33 2.176 2 047 1858* 2.49 4.19 7.90 35236 2.373 2 158 1862* 2.65 6.08 6.32 31 154 2.188 2.145 1859* 2.54 6.007.93 .32 230 2.362 2.276 1868* 2.60 8.05 6.00 .30 234 2.369 2.369 1871*2.46 7.99 8.03 .29 242 2.384 2.427

Note: All heats contained from 15 to 19% Cr; 15% Max. C; .10% Max. N;and normal residual impurities. (1) Inches of holes drilled. average ofthree tests.

(2) Logarithm of values in column V1. (3) Values in column Vllstandardized to .30 sulfur level by the formula: Logarithm of Drill Life4.30 (%S .30) =standardized logarithm of drill life. (4) Residual. i.e.,about .196.

Of the ea listed in Table the 23 marked h an 65 each of these 23 heats,as well as various averages, is asterisk were melted as a group havingcontrolled analtabulated in Table 11 below, and these values were usedyses, particularly of manganese, copper and nickel, for to plot thegraphs of FIGS. 1 to 3.

TABLE II Log Drill Life 23 Heats Adjusted to .30% Sulfur by the FormulaLog D.L. 4.30(% S .30)

6% Ni 8% Ni Total 4% Mn 6% Mn 8%Mn Total 4%Mn 6%Mn 8%Mn Total 4%Mn 6%Mn8%Mn Total (1846) (1849) (1850) (1874) (1848) (1851) Avg. 1.892 1.8401.562 1.871 2.165 1.866 1% Cu 1.992 1.935 2.255 6.182 1.677 2.150 2.2206.047 3.669 4.085 4.475 12.229

(1852) (1860) (1865) (1865) (1863) (1869) Avg. 2.061 2.016 1.834 2.0422.238 2.038 2% Cu 2.025 2.190 4.215 1.915 2.206 2.198 6.319 3.940 4.3962.198 10.534

(1854) (1861) (1857) (1864) (1870) Avg. 2.108 2.106 1.970 2.198 2.1982.107 2.5% Cu 2.047 2.145 2.369 6.561 2.158 2.276 2.427 6.861 4.2054.421 4.796 13.422

(1855) (1862) (1868) (1858) (1859) (1871) Avg. 2.187 2.287 2.102 2.2102.398 2.237 Total 7.791 8.012 6.831 22.364 7.148 8.632 8.968 24.74814.939 16.644 15.799 47.382 Avg. 1.948 2.003 2.277 2.058 1.787 2.1582.242 2.062 1.867 2.080 2.257 2.060

Note: Heat Numbers in Parenlheses.

It should be noted that the machinability value used in Table II and inthe figures is the logarithm of the drill life standardized to 0.30percent sulfur. The logarithm of the drill life was chosen since thiswill tend to equalize variations at both high and low values. Theselogarithms were then corrected to a standarized sulfur content (0.30percent sulfur was chosen since this is commercially the minimumrequired to obtain maximum machinability in austenitic alloys) tocompensate for variation due to different sulfur contents, it beingrecognized that small variations in sulfur have large effects on themachinability. The correction factor for sulfur was determinedempirically using the heats in Table I. The levels of the elementsreported in Table II represent the nominal levels of each, although theactual average levels of copper are given in parentheses since they dodeviate somewhat from the nominal values. Also, in the figures thevarious lines are labeled with the nominal values, and in fact themanganese and nickel values in FIGS. 2 and 3 are plotted at the nominalamounts since, in the case of these two elements, the nominal values areclose to the actual; however, in FIG. 1 the copper values are plotted atthe average because of the variation thereof from the nominal.

Referring now to FIG. 1(a), it can be seen that at all manganese levelswhen the copper is increased from zero to about 2.5 percent, asubstantial increase in drill life occurs, which means the steel is moreeasily machined at the higher copper levels; also, the machinability isincreased at higher manganese levels, as shown by the location of thelines for the various levels of manganese. The composite line shown inFIG. 1(b) shows also the effect of increasing copper as increasing themachinability at the average manganese content; FIG. 2(a) shows that atany given copper level, increasing the percentage of manganese in thesteel substantially increases the drill life, thus indicating that athigher manganese levels the ease of machining is substantiallyincreased; also, the location of the lines for the various levels ofcopper shows increased machinability at higher copper levels; FIG. 2(b)shows also the effect of increasing manganese as increasing themachinability at the average copper percentage; FIG. 3(a) shows that atany given copper level, increasing the nickel content does not have anysignificant effect on the machinability of the stainless steel, but thatthe machinability at any nickel level is higher with more copper, andFIG. 3(b) shows this lack of effect of nickel on machinability ataverage copper levels.

The results of the machinability tests on the various alloys listed inTable I, and particularly the controlled group also listed in Table IIand plotted in the figures, indicate that the best machining compositionis a composition wherein the manganese and copper are relatively highwhereas the nickel content is relatively unimportant with respect tomachinability. It has been found, however, that at this optimum highlevel of manganese and copper, the composition must be controlled sothat the percentage of copper does not exceed 3.85 O.l8(% Mn 55/32% S);if the copper content exceeds this value, the alloy cannot be properlyhot worked because of cracking and edge checking. In fact, the billetsfrom heats 1868 and 1871, the composition of which approaches thislimit, gave some indication of edge checking during processing which, ifit had been any more severe, would have rendered the materialunsuitable. It has further been found, and an examination of Table Iwill show, that when the manganese content exceeds about 6 percent thereis a tendency for the alloy to retain less than 0.30 percent sulfur,which will materially reduce its free machining characteristics sincesulfur is the major contributor to the free machining characteristics ofthe alloy. It is known that more sulfur can be retained in the finalproduct if the melting temperature is raised; however, this introducesadditional problems of increased erosion of furnace and ladlerefractories which, in turn, may require costly changes in melting,tapping and teeming practices. Hence, when maximum free machiningproperties are desired, the sulfur should be in the range of 0.30percent to 0.40 percent, which means the manganese content cannot exceedabout 6 percent if conventional furnace and ladle practices are to befollowed. However, the machinability of the alloys containing manganeseand copper is so superior to that of AISI Type 303 which contains nocopper and very little manganese, the sulfur content can actually belowered to the range of about 0.15 percent and machinability comparableto that of AIS] 303 can be obtained. For example, heats 1859, 1868 and1858, which are within the scopeof this invention, have a drill lifeabout four times as great as heats 1727 and 1426, which are examples ofconventional AISI Type 303 free machining stainless steel. Whereincreased hot and cold workability, as well as increased corrosionresistance, is desired, and where machinability merely comparable toType 303 is desired, greater manganese contents can be used with acorresponding reduction in the amount of sulfur, it being understoodthat the lower the sulfur value, the greater the corrosion resistanceand the greater the workability the alloy will have, but it will havedecreased machining characteristics.

It is also known that the alloying elements of stainless steelscontaining manganese, nickel and copper must be properly balanced toprevent the formation of excessive delta ferrite during hot rolling.When excessive delta ferrite is formed during hot rolling, the ingot orbloom cannot be properly hot worked; the relationship of the alloyingelements to the formation of delta ferrite must be such that the deltaferrite-forming characteristic or potential is less than 10 according tothe formula:

delta ferrite potential Cr 1.5(% Si) .87[30(% C 7c N) With respect tothe composition limits, the chromium content cannot be below about 10percent in order to achieve proper corrosion resistance, and thechromium content should not exceed about percent since more than thiswould require excessive amounts of other elements to prevent theformation of delta ferrite, and higher amounts of the other elementscould lead to hot shortness problems in the balance of copper andmanganese and increased expense with respect to nickel. Hence, the broadlimits for the chromium are about 10 to 20 percent. If there is lessthan about 4 nickel, the manganese and/or copper contents would have tobe increased to obtain the stability with respect to the formation ofexcessive delta ferrite. This would tend to make the alloy hot short ifenough manganese and/or copper were added to compensate for the reducedamount of nickel, and also would reduce the amount of sulfur retained ifthe manganese is increased. More than about 13 percent nickel addsneedlessly and substantially to the cost of the alloyv There must be atleast 2 percent manganese, since less than this would require excessiveamounts of nickel for stability and corrosion resistance, adding to thecost of the alloy but not improving its machinability, or excessivecopper which would tend to make the alloy hot short if the desiredstability and-machinability are to be obtained; also, more than 2percent manganese is required since it adds substantially to themachinability of the alloy. There cannot be more than about 10 percentmanganese, since the amount of copper that could be used would becorrespondingly reduced because of hot shortness problems, and alsothere is the problem of reduced sulfur retention. With less than about0.50 percent copper, the machinability is greatly reduced, which wouldrequire excessive amounts of manganese to compensate for this which, inturn, reduces the amount of sulfur retained. With more than about 3percent copper, the alloy tends to be hot short unless the manganesecontent is maintained low, and the copper has a lesser effect on thesuppression of delta ferrite than manganese or nickel. When the carbonand nitrogen contents exceed about 0.15 percent and 0.10 percentrespectively, they adversely affecting the corro- SlOn reslstance.

With an alloy falling within the broad limits described above andwherein the delta ferrite-forming potential is less than 10 percent andthe copper does not exceed 3.85 0.18(% Mn 55/32%S), an austeniticstainless steel of superior machining characteristics is produced. Aswas indicated previously, the principal element relied on for ease ofmachining is sulfur. As can be seen from Table I, where the sulfur is inthe range of 0.30 to 0.40 percent, an alloy having a machinabilityrating based on drill life three to four times as good as AlSl Type 303is produced, and hence, for superior machinability sulfur contents ofbetween 0.30 percent and 0.40 percent are desired. Where increasedworkability and corrosion resistance are desired, a sulfur content ofbetween 0.10 percent and 0.30 percent is preferred It is easier toachieve an economic balance of elements within a substantially narrowermelting range. This narrower or preferred range is as follows: about0.08 percent maximum carbon, up to 1 percent silicon from about 4 to 6percent manganese where sulfur in the range of 0.30 to 0.40 percent isrequired, and 6 to 8 percent manganese where sulfur in the range of 0.10to 0.30 percent is required, from 5 to 7 percent nickel, from 14 to 18percent chromium, and from 1.5 to 2.5 percent copper. Within this narrowrange it is still necessary, though, to keep the delta ferrite-formingpotential at less than 10, and the copper-manganese balance must bemaintained according to the formulae given above for the alloy to bewithin the scope of this invention.

Although several embodiments of this invention have been shown anddescribed, various adaptations and modofications may be made withoutdeparting from the scope of the appended claims.

I claim:

11. A free machining, austenitic stainless steel consisting essentiallyof from a trace up to 0.15 percent carbon, from 2 to 10 percentmanganese, from 4 to 13 percent nickel, from 10 to 20% chromium, from0.5 to 3 percent copper, from 0.10 to 0.40 percent sulfur, 2 percentmaximum silicon, and 0.10 percent maximum nitrogen, balance essentiallyiron and residual impurities, the constituents being controlled so thatthe delta ferrite forming characteristic is less than 10 according tothe formula:

delta ferrite potential Cr 1.5(% Si) .87 [30(% C N) and wherein theamount of copper is controlled so that it does not exceed 3.85 0.18 Mn-55/32% S).

2. A free machining, austenitic stainless steel, according to claim 1,consisting essentially of from a trace up to 0.15 percent carbon, from 4to 6 percent manganese, from 4 to 13 percent nickel, from 10 to 20percent chromium, from 0.5 to 3 percent copper, from 0.30 to 0.40percent sulfur, 2 percent maximum silicon,

0.10 percent maximum nitrogen, balance essentially iron and residualimpurities.

3. A free machining, austenitic stainless steel according to claim 1consisting essentially of from a trace up to 0.15 percent carbon, from 6to 8 percent manganese, from 4 to 13 percent nickel, from to percentchromium, from 0.5 to 3 percent copper, from 0.10 to 0.40 percentsulfur, 2 percent maximum silicon, 0.10 percent maximum nitrogen,balance essentially iron and residual impurities.

4. A free machining, austenitic stainless steel according to claim 1consisting essentially of from a trace up to 0.08 percent carbon, from 4to 8 percent manganese, from 5 to 7 percent nickel, from 14 to 18percent chromium, from 1.5 to 2.5 percent copper, from 0.10 to 0.40percent sulfur, 1 percent maximum silicon, 0.10 percent maximumnitrogen, balance essentially iron and residual impurities.

5. A free machining, austenitic stainless steel according to claim 1consisting essentially of from a trace up to 0.08 percent carbon, from 4to 6 percent manganese, from 5 to 7 nickel, from 14 to 18 percentchromium, from 1.5 to 2.5 percent copper, from 0.30 to 0.40 percentsulfur, 1 percent maximum silicon, 0.10 percent maximum nitrogen,balance essentially iron and residual impurities.

6. A free machining, austenitic stainless steel according to claim 1consisting essentially of from a trace up to 0.08 percent carbon, from 6to 8 percent manganese, from 5 to 7 percent nickel, from 14 to 18percent chromium, from 1.5 to 2.5 percent copper, from 0.10 to 0.30percent sulfur, 1 percent maximum silicon, 0.10 percent maximumnitrogen, balance essentially iron and residual impurities.

1. A FREE MACHINING, AUSTENITIC STAINLESS STEEL CONSISTING ESSENTIALLYOF FROM A TRACE UP TO 0.15 PERCENT CARBON, FROM 2 TO 10 PERCENTMANGANESE, FROM 4 YO 13 PERCENT NICKEL, FROM 10 TO 20% CHROMIUM, FROM0.5 TO 3 PERCENT COPPER, FROM 0.10 TO 0.40 PERCENT SULFUR, 2 PERCENTMAXIMUM SILICON, AND 0.10 PERCENT MAXIMUM NITROGEN, BALANCE ESSENTIALLYIRON AND RESIDUAL IMPURTIES, THE CONSTITUENTS BEING CONTROLLED SO THATTHE DELTA FERRITE FORMING CHARACTERISTIC IS LESS THAN 10 ACCORDING TOTHE FORMULA:
 2. A free machining, austenitic stainless steel, accordingto claim 1, consisting essentially of from a trace up to 0.15 percentcarbon, from 4 to 6 percent manganese, from 4 to 13 percent nickel, from10 to 20 percent chromium, from 0.5 to 3 percent copper, from 0.30 to0.40 percent sulfur, 2 percent maximum silicon, 0.10 percent maximumnitrogen, balance essentially iron and residual impurities.
 3. A freemachining, austenitic stainless steel according to claim 1 consistingessentially of from a trace up to 0.15 percent carbon, from 6 to 8percent manganese, from 4 to 13 percent nickel, from 10 to 20 percentchromium, from 0.5 to 3 percent copper, from 0.10 to 0.40 percentsulfur, 2 percent maximum silicon, 0.10 percent maximum nitrogen,balance essentially iron and residual impurities.
 4. A free machining,austenitic stainless steel according to claim 1 consisting essentiallyof from a trace up to 0.08 percent carbon, from 4 to 8 percentmanganese, from 5 to 7 percent nickel, from 14 to 18 percent chromium,from 1.5 to 2.5 percent copper, from 0.10 to 0.40 percent sulfur, 1percent maximum silicon, 0.10 percent maximum nitrogen, balanceessentially iron and residual impurities.
 5. A free machining,austenitic stainless steel according to claim 1 consisting essentiallyof from a trace up to 0.08 percent carbon, from 4 to 6 percentmanganese, from 5 to 7 nickel, from 14 to 18 percent chromium, from 1.5to 2.5 percent copper, from 0.30 to 0.40 PERCENT sulfur, 1 percentmaximum silicon, 0.10 percent maximum nitrogen, balance essentially ironand residual impurities.
 6. A free machining, austenitic stainless steelaccording to claim 1 consisting essentially of from a trace up to 0.08percent carbon, from 6 to 8 percent manganese, from 5 to 7 percentnickel, from 14 to 18 percent chromium, from 1.5 to 2.5 percent copper,from 0.10 to 0.30 percent sulfur, 1 percent maximum silicon, 0.10percent maximum nitrogen, balance essentially iron and residualimpurities.